A004122 Generalized weak orders on n points. (Formerly M2064)

2, 13, 123, 1546, 24283, 457699, 10064848, 252945467, 7151532895, 224661610888, 7763387794649, 292659248485051, 11951855446598278, 525645673381008537, 24769319755329986599, 1244984053628241578058, 66487872534167725541751

Offset

1,1

References

I. P. Goulden and D. M. Jackson, Combinatorial Enumeration, John Wiley and Sons, N.Y., 1983.

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

C. G. Wagner, Enumeration of generalized weak orders. Arch. Math. (Basel) 39 (1982), no. 2, 147-152.

Links

T. D. Noe, Table of n, a(n) for n = 1..100

C. G. Wagner, Enumeration of generalized weak orders, Preprint, 1980. [Annotated scanned copy]

C. G. Wagner and N. J. A. Sloane, Correspondence, 1980

Formula

E.g.f. : 1/(2-exp(x)*exp(exp(x)-1)).

Mathematica

With[{nn=20}, Rest[CoefficientList[Series[1/(2-Exp[x]Exp[Exp[x]-1]), {x, 0, nn}], x] Range[0, nn]!]] (* Harvey P. Dale, Nov 05 2011 *)

Crossrefs

Cf. A004121, A004123, A000670.

Sequence in context: A292437 A317196 A192460 * A359124 A086630 A151361

Adjacent sequences: A004119 A004120 A004121 * A004123 A004124 A004125

Keyword

nonn,nice,easy

Author

N. J. A. Sloane

Extensions

Formula and more terms from Vladeta Jovovic, Mar 27 2001

Status

approved